This invention relates to novel reactive urethane compounds, their synthesis and end-uses particularly in automotive coatings with improved chemical resistance and mechanical properties. In a preferred embodiment, the invention relates to automotive paint compositions having hydroxy functional binders and a cross-linking agent such as melamine, urea or benzoguanamine formaldehyde resins (so called aminoplast resins) and/or blocked polyisocyanates (when the curing temperature is relatively high, i.e., above 80xc2x0 C.) in a one-pack formulation or polyisocyanates (when the crosslinking needs to take place at lower temperatures) in 2-pack formulations.
Acrylic polyols are typically used in topcoat formulation because of the outstanding durability. However,the mechanical properties like chip resistance and scratch resistance are poor. Polyester polyols do give better mechanical properties but are poor for chemical resistance, specifically acid etch resistance. Polyurethane polyols combine excellent chemical and mechanical properties with very good durability.
U.S. Pat. Nos. 4,485,228 and 4,540,766 describe high solids coating systems based on low molecular weight polyester urethane polyols. More particularly U.S. Pat. No. 4,485,228 describes compositions crosslinked with polyisocyanates in a 2-pack system while U.S. Pat. No. 4,540,766 describes 1-pack systems crosslinked with polyisocyanates. In those patents the polyester urethane polyols are prepared by a stoichiometric excess of a polyester polyol with a polyisocyanate to avoid high molecular weight build-up during the synthesis.
U.S. Pat. No. 4,543,405 refers to low molecular weight polyurethane polyols which are prepared from a polyisocyanate with a large excess of a polyol. This excess of polyol is, after the reaction has completed, distilled-off. In related U.S. Pat. Nos. 4,540,771 and 4,605,724 the polyester polyols for the polyurethane polyols are produced from polycarboxylic acids or lactone with low molecular weight polyol, wherein the excess polyol is also removed by distillation. The disadvantage of the procedure in above mentioned references is the distillation step which is not economic.
EP 0 661 316 and EP 0 866 082 relate to reactive urea/urethane compounds, the process for preparation and coatings based on those compounds which are prepared from the reaction of a polyisocyanate with a secondary amine containing one or two hydroxyl groups. The advantage of this process is the fact that the reaction of the isocyanate group preferentially goes with the secondary amine group to form low molecular weight hydroxyfunctional urethane-urea adducts. The disadvantage is that urea groups have a strong hydrogen bonding character which leads to limited solubility and relatively high solution viscosity. U.S. Pat. No. 5,130,405 and U.S. Pat. No. 5,175,227 are directed to high solids coating compositions containing polyurethane oligomers derived from the reaction of symmetrical and unsymmetrical 1,3-diols and polyisocyanates. Such compounds do have very low molecular weight with high hydroxyl values. Low molecular weight oligomers with high hydroxyl values act as strong slow solvents and many times negatively influence the appearance of automotive clear coats. EP 0 767 230, EP 0 767 187, EP 0 767 226, EP 0 767 228, EP 0 767 231, EP 0 767 229, EP 0 767 232 and EP 0 767 227 all relate to curable coating compositions having carbamate functional groups for crosslinking purposes. The carbamate functional groups can be represented by
xe2x80x94Oxe2x80x94COxe2x80x94NHxe2x80x94R
wherein R is hydrogen or alkyl, preferably Cl -C4 alkyl and more preferably hydrogen. Primary carbarnates (R=hydrogen) negatively influence solution viscosity due to strong hydrogen bonding and secondary carbamates need specific catalysis to react with amino resins.
U.S. Pat. No. 4,820,830 relates to hydroxyalkyl carbamates prepared by reacting cyclic carbonates with diamines. Such hydroxyalkyl carbamates have many times limited solubility and compatibility due to high secondary carbamate content. U.S. Pat. No. 4,883,854 describes polyurethanes derived from hydroxyalkyl carbamates which are synthesized from polyamines with at least two amine groups and cyclic carbonates. There is no teaching on the reaction products of mono secondary amines with cyclic carbonates to form the hydroxyl functional carbamates and the further use in the synthesis of branched hydroxyl functional oligomers with controlled molecular weight distribution. U.S. Pat. No. 4,542,173 relates to self-crosslinkable binders containing at least to hydroxyalkyl carbamate groups with a secondary carbamate group. U.S. Pat. No. 5,175,231 relates to urethane oligomers with an amine functional group.
It is therefore desirable to find a method for preparing highly branched hydroxy functional urethane adducts with a controlled molecular weight distribution and essentially free from primary carbamate and urea groups. Such compounds would provide coating compositions with a good combination of low solution viscosity (low VOC), excellent chemical resistance, mechanical properties and outdoor durability.
Hydroxy functional urethane compounds comprising the reaction product of:
a) a hydroxy functional urethane intermediate containing a tertiary carbamate group prepared by reaction of a cyclic 5-ring carbonate with a beta-hydroxy functional, secondary amine, said intermediate represented by the formula: 
xe2x80x83wherein
R1 and R2=hydrogen, alkyl, cycloalkyl or a residue R6xe2x80x94Oxe2x80x94 or R6xe2x80x94COxe2x80x94Oxe2x80x94 with R6;
R6 =an alkyl, cycloalkyl or benzylic group having up to 18 carbon atoms;
R4 and R5=hydrogen or alkyl group containing eventually a hydroxyl group; and
R3=alkyl, cycloalkyl or benzylic group eventually containing an ether linkage and/or a hydroxyl group, or HOxe2x80x94CH(R1)xe2x80x94CH(R2)xe2x80x94 with
b) a compound with at least 2 isocyanate groups.
Such hydroxy functional urethanes can be used in automotive coatings to improve the mechanical properties and chemical resistance of such coatings.
The present invention relates to novel hydroxyl functional binders which comprise the reaction product of polyisocyanates with a tertiary carbamate having at least two hydroxyl groups. The coating compositions based on those binders offer improved mechanical properties and chemical resistance. The tertiary carbamate with at least two hydroxyl groups can be represented as: 
wherein
R1 and R2=hydrogen, alkyl, cycloalkyl or a residue R6xe2x80x94Oxe2x80x94 or R6xe2x80x94COxe2x80x94Oxe2x80x94 with R6;
R6=an alkyl, cycloalkyl or benzylic group having up to 18 carbon atoms;
R4 and R5=hydrogen or alkyl group containing eventually a hydroxyl group; and
R3=alkyl, cycloalkyl or benzylic group eventually containing an ether linkage and/or a hydroxyl group, or HOxe2x80x94CH(R1)xe2x80x94CH(R2)xe2x80x94
In particularly preferred embodiments, R1 is CH3 or H; R2 is H, R3 is HOxe2x80x94CH(CH2)xe2x80x94CH2xe2x80x94 or CH3(CH2)3xe2x80x94; R4 is H; and R5 is H, CH3, or C2H5.
Such carbamates can be prepared by the reaction of a secondary amine with a cyclic 5-ring carbonate. Examples of 5-ring carbonates include ethylene carbonate, propylene carbonate, butylene carbonate and glycerine carbonate. Examples of secondary amines are alkyl, benzyl and cycloalkyl-ethanolamines and alkyl-propanol amines as methyl ethanolamine, n-butyl aminoethanol, hexyl aminoethanol, benzyl aminoethanol, cyclohexyl aminoethanol, methyl propanolamine, n-butyl propanolamine, cyclohexyl propanolamine and benzyl propanolamine.
Such compounds are typically prepared by reaction of cyclic oxides as ethyleneoxide or propyleneoxide with a primary amine. Examples of bis-hydroxyl functional secondary amines are diethanolamine and diisopropanolamine. Secondary amines can also be prepared from the reaction of primary amines with other cyclic three-member oxides as n-butyleneoxide, cyclohexeneoxide, i-butyleneoxide and derivatives as monoepoxy ethers and monoepoxy esters. Examples of monoepoxy esters are glycidyl esters of mono acids as acetic acid, butyric acid, isobutyric acid, pivalic acid, versatic acid and C9 and C10 alpha branched fatty acids available from Shell. Examples of monoepoxy ethers are glycidyl ethers of phenyl, n-butyl, lauryl, t-butylphenyl and cyclohexyl.
The reaction of the secondary amine can be performed at room temperature up to 200xc2x0 C., preferably between 40xc2x0 C. and 150xc2x0 C. Solvents can eventually be used in this reaction. Examples of solvents are alcohols, ketones, esters, amides, and aliphatic or aromatic hydrocarbons. Typical examples are methanol, n-butanol, s-butanol, t-butanol, n-propanol, i-propanol, n-hexanol, 2-ethyl hexanol, laurylalcohol, acetone, methyl ethyl ketone, isobutyl methyl ketone, methyl amyl ketone, toluene, xylene, Solvesso(copyright) 100, Solvesso(copyright) 150, Solvesso(copyright) 200 (trade name of Exxon Corporation), heptane, mineral spirits, n-methyl pyrrolidone, ethylacetate, n-butylacetate, i-butylacetate, t-butylacetate, 2-ethyl hexylacetate, propylene glycol, ethylene glycol, propylene glycol n-butyl ether, propylene glycol n-butyl ether acetate, diethylene glycol and diethyleneglycol diacetate.
Catalysts can be used in the synthesis of the tertiary carbamate intermediate as e.g., tin and zinc salts (dibutyl tin dilaurate, dibutyl tin oxide, tin octoate, zinc octoate), bases (potassium hydroxide, sodium hydroxide, magnesium hydroxide) and acids (acetic acid, toluene sulfonic acid, dodecyl benzene sulfonic acid, phenyl acid phosphate).
In a next step, the hydroxyl functional tertiary carbamate intermediate is reacted with a compound having at least two isocyanate groups. Example of such compounds are diisocyanates as e.g., hexamethylene diisocyanate, isophorone diisocyanate, toluene diisocyanate, 3,3xe2x80x2,5-trimethyl hexamethylene diisocyanate, meta and para tetramethyl xylene diisocyanate, 4,4xe2x80x2-dicyclohexylmethane diisocyanate (Desmodur(copyright) W from Bayer AG) and 4,4xe2x80x2-diphenylmethane diisocyanate. Polyfunctional isocyanates derived from the diisocyanates can also be used as e.g., the cyclotrimer of isophorone diisocyanate and hexamethylene diisocyanate, the biuret of hexamethylene diisocyanate, the uretdion dimer of hexamethylene diisocyanate (i.e., the 4 ring dimerization product of NCO with NCO), the adducts of polyols (e.g., trimethylol propane) with an excess of diisocyanate.
A polyisocyanate can also be formed by reaction of a diisocyanate excess with a compound having at least two reactive groups versus the isocyanate, preferably having at least two hydroxyl groups. Such compounds can be diols or polyols derived from polyesters, polycarbonates, polyethers, polyacrylics and polyisocyanates.
The novel urethanes which are the final reaction products of the tertiary carbamate intermediate with the polyisocyanates can be used in paint compositions in which the reaction product is crosslinked with an amino resin or polyisocyanate which can be blocked or unblocked. It has been found that cured films from above paint compositions have good chemical resistance and mechanical properties like hardness, flexibility, scratch and chip resistance. Specifically, automotive clearcoats made with these novel urethanes demonstrate significant improvements in acid etch and scratch resistance. In one pack clearcoats the crosslinkers are typically melamine formaldehyde adducts etherified with alcohols as methanol, isobutanol or n-butanol. Blocked polyisocyanates can also be used as e.g., methylethyl ketoxime or dimethyl pyrazole blocked trimers of hexamethylene diisocyanate or isophorone diisocyanate. In such one pack clearcoats, the curing temperature is above 80xc2x0 C. typically between 100xc2x0 C. and 180xc2x0 C. The clearcoats may contain additives to improve properties as e.g., application (sagging), flow, wetting, durability. Other polymers can be used in the clearcoats to improve specific properties which include acrylics, polyesters, vinyls, polyurethanes, polycarbonates, alkyds and polysilanes.
Catalysts can be added to speed-up the curing reaction as e.g. toluene sulfonic acid, phenyl acid phosphate, dibutyl tin dilaurate. Other one pack automotive paint compositions include primers, basecoats and pigmented topcoats. Those compositions contain regular pigments and extenders which can be organic or inorganic. Examples of pigments include titanium dioxide, barium sulfate, talc, aluminum silicate, phtalocyanines, quinacridones, carbon black, aluminum flakes, mica flakes and lead chromate. In refinish applications, the curing temperature of the final coating is ambient up to 80xc2x0 C. maximum. The reaction products of the present invention can be used is two pack coatings in which the crosslinker is added to the paint containing the reaction product prior to application. Typical crosslinkers used in two component paints are polyisocyanates. Specific examples are the biuret and cyclotrimer of hexamethylene diisocyanate and isophorone diisocyanate.
Coating compositions can be coated on the article by any number of techniques well-known in the art. These include, for example, spray coating, dip coating, roll coating, curtain coating and the like. For automotive body panels, spray coating is preferred. The substrate can be any substrate onto which a coating formulation can be applied and cured. Preferably the substrate is a metallic or polymeric panel suitable as an automotive body panel.